Reference will be made in this application to layer-2. Layer-2 is sometimes called the link layer. In addition to the link layer, there are other layers including the network layer, the physical layer and the optical layer. The traditional roll of layer-2 is switching. Layer-2 services (such as frame relay, ATM, Ethernet) can be emulated over an Internet Protocol (IP) or Multi-Protocol Label Switching (MPLS) backbone by encapsulating the layer-2 Packet Data Units (PDUs) and then transmitting them over pseudo-wires.
Virtual Private LAN Service (VPLS) is an internet-based multipoint-to-multipoint Layer-2 Virtual Private Network (L2VPN). (Layer-2 virtual private network is a term known to those skilled in the art, and it is a term having broader meaning than virtual private LAN service.) With VPLS, multiple Ethernet LAN sites can be connected to each other across an MPLS backbone. To the customer, all sites that are interconnected by VPLS appear to be on the same Ethernet LAN (even though traffic travels across a service provide network).
The protocol for assigning and distributing a pseudo-wire label is called Label Distribution Protocol (LDP). LDP is discussed in detail in “RFC 3036: LDP Specification”, Andersson et al. (available through http://ietf.org/), the entire contents of which are incorporated herein by reference. In RFC 3036, an LDP session is described as a session in which two LDP peers use LDP to exchange label/FEC mapping information.
There currently exists VPLS LDP (VPLS LDP is LDP within a VPLS) based solutions that do not use an auto-discovery mechanism. These solutions are characterized in that the operator needs to configure both sides of the pseudo-wire making up the VPLS service on both ends of the Provider Edge devices (PEs) where each PE has a priori knowledge of the remote PE pseudo-wire information. This is known as a double-sided provisioning model. Alternatively, each PE will signal to the remote PE the VPLS information, and if the remote PE does not have a VPLS in common with that PE it will just ignore this information.
A possible disadvantage associated with the above-mentioned methods is that a PE will allocate resources (such as memory and CPU) for VPLS information that will end up being discarded. Another possible disadvantage is that the network is congested with VPLS information that will end up being discarded. Yet another possible disadvantage is LDP sessions are established between PEs that may never have any VPLS in common.